From 3848e96edf4788f772d83990022fa7023a233d83 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Tue, 8 Mar 2022 13:42:17 +1100 Subject: [PATCH] SUNRPC: avoid race between mod_timer() and del_timer_sync() xprt_destory() claims XPRT_LOCKED and then calls del_timer_sync(). Both xprt_unlock_connect() and xprt_release() call ->release_xprt() which drops XPRT_LOCKED and *then* xprt_schedule_autodisconnect() which calls mod_timer(). This may result in mod_timer() being called *after* del_timer_sync(). When this happens, the timer may fire long after the xprt has been freed, and run_timer_softirq() will probably crash. The pairing of ->release_xprt() and xprt_schedule_autodisconnect() is always called under ->transport_lock. So if we take ->transport_lock to call del_timer_sync(), we can be sure that mod_timer() will run first (if it runs at all). Cc: stable@vger.kernel.org Signed-off-by: NeilBrown Signed-off-by: Trond Myklebust --- net/sunrpc/xprt.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c index 744c6c1d536f..880bfe8dc7f6 100644 --- a/net/sunrpc/xprt.c +++ b/net/sunrpc/xprt.c @@ -2104,7 +2104,14 @@ static void xprt_destroy(struct rpc_xprt *xprt) */ wait_on_bit_lock(&xprt->state, XPRT_LOCKED, TASK_UNINTERRUPTIBLE); + /* + * xprt_schedule_autodisconnect() can run after XPRT_LOCKED + * is cleared. We use ->transport_lock to ensure the mod_timer() + * can only run *before* del_time_sync(), never after. + */ + spin_lock(&xprt->transport_lock); del_timer_sync(&xprt->timer); + spin_unlock(&xprt->transport_lock); /* * Destroy sockets etc from the system workqueue so they can